锰矿修复区植物生态系统自由能与化学势分析

Gibbs free energy and chemical potentials of plant communities in a manganeseore tailing site undergoing ecological restoration

基于热力学理论建立了生态系统Gibbs自由能方程,用以计算湘潭锰矿生态修复区植被系统的自由能(G)和物种化学势(μ)。生态修复区(及对照区)以泡桐(Paulownia fortunei)和栾树(Koelreuteria bipinnata)作为建群植物,总面积为4 hm^2,修复区泡桐和栾树的根际施用了含有自试验点废弃矿渣中筛选出的耐性菌株的有机菌肥,目的是为植物生长提供必要养分和降低根际土壤重金属毒性,对照区泡桐和栾树的根际施用了等量的化肥。泡桐和栾树种植后5 a期间,修复区与对照区均自然萌发生长了许多本土植物种类。试验结果表明,修复区植物种类数达到48,为对照区的3.7倍;修复区的总生物量、锰吸收量分别达到23324 kg/hm^2和4280 g/hm^2,为对照区对应值的20.6和2.6倍;修复区系统自由能G远远大于对照区的值,说明有机菌肥具有显著的改良污染土壤根际环境的效果。修复区和对照区植物种类之间的化学势μ均存在显著差异(P<0.001),μ值差异范围分别为-3.79—6.76和-3.42—3.59,该一差异反映不同物种适应和修复锰污染环境的能力。G和μ值包含了生态系统生产力、生物多样性,植物种类生长势、重金属富集能力、生态学行为等综合信息,能反映生态系统与立地环境的关系和修复植物的生态学特性,可作为重金属污染区植被修复效果评价和修复植物筛选的重要指标。

Matter and energy exchanges constitute the basis of ecological processes. Therefore, ecosystems can be regarded as open thermodynamic systems, with bio-species as key components. The changes in ecosystem states can therefore be measured and compared in terms of Gibbs free energy （G） and chemical potential （/x）. Based on thermodynamic theories, an ecosystem Gibbs free energy model was established for calculating the changes in G of plant communities and p of the plant species, at an ecological restoration site of manganese-ore tailing in the Xiangtan region. The total area of the experimental site, including the control plot, was 4 hectares, which was covered with Paulownia fortunei and Koelreuteria bipinnata as the dominant, transplanted, wood species. The rooting areas of the wood species at the experimental site were amended with organic manure, containing a tolerant bacterium strain isolated from the experimental site＇s mining waste. Organic manure application was undertaken not only to provide necessary nutrients for plant growth, but also to improve the root growth conditions by reducing the metal toxicity in the rhizosphere. The wood plant species were screened first, and theamending effects of the organic project. For comparison purposes year period after transplanting th manure were tested in pot experiments before initiating , an equivalent amount of chemical fertilizers was applied e wood species to the site, native plant species naturally the on-site ecological restoration to the control plot. Within a five- germinated as well, and grew in both the restoration and control sites. Soil and plant samples were collected and analyzed using standard methods. The number of plant species was counted, and the density of each species was estimated at the site. Furthermore, the cover percentage, biomass quantity, and manganese uptake of each plant species were calculated. The number of plant species at the restoration site was 48, which was 4 times that of the control plot. The total dry biomass and manganese uptake at the restoration site was 23,324 kg/hm2 and 4,280 g/hm2, respectively. This was respectively 20.6, and 2.6 times as high as in the control plot. In addition, the plant community＇s total Gibbs free energy was significantly higher at the restoration site than at the control site. These results indicate that the application of organic manure improved the root growth conditions of the contaminated soil, and that the effects were significant. There were also significant differences in chemical potentials among the plant species at both the restoration and control sites （P 〈 0.001 ）. The/x values for different plant species ranged between -3.79 to 6.76, and -3.42 to 3.59, respectively, at the restoration and control sites. The/x value reflects the ability of plant species not only to adapt, but also to restore the metal-contaminated environment. As ecosystem properties, both G and/z are functions of biomass, manganese uptake, density, and the number of plant species. The values of G furthermore, comprise integrated information on the productivity and biodiversity of the ecosystem. The values of/z concern the growth potential regarding , heavy metal accumulation capacity, and relevant ecological characteristics of the plant species their mutual competition, inhibition, and symbiosis behaviors under given site conditions. In comparison with traditionally applied hyperaccumulators and biodiversity indices, the G and/.t values were found to be appropriate parameters for evaluating the impacts of a site＇s environment on ecosystem growth. Furthermore, they proved suitable for analyzing the ecological behaviors of the remediation plants. In sum, both G and/x values can be used as important indices for determining the effects of ecological restoration in heavy metal contaminated areas, as well as for the screening of phytoremediation plant species.